Intraluminal, vascular stents have been widely used as solid mechanical, structural supports to maintain an open lumen following balloon angioplasty. However, there is a great deal of evidence that suggests that the mechanical environment in arteries plays an important role in the development and progression of cardiovascular disease. The presence of a vascular stent within the lumen of a vessel alters fluid flow patterns through the vessel. Accordingly, the use of stents may significantly influence the incidence of cardiovascular disease following balloon angioplasty due to changes in the mechanical environment caused by the stent.
From a mechanical perspective, arteries are quite complex. The arterial wall is subjected to internal pressurization that also induces large, circumferentially oriented stresses. In addition, the flow of blood through the artery creates a frictional shearing stress in the direction of flow. All of these stresses depend heavily on the arterial geometry, and thus vary greatly throughout the cardiovascular system. The presence of arterial grafts or stents provokes changes in these mechanical factors that may be important in determining the success of such grafts or stents.
Data are now emerging that implicate a mismatch in vessel compliance (i.e., the ratio of a change in vessel cross-sectional area to a change in vessel pressure) between the vascular graft or stent and the host vessel as a culprit in neointimal hyperplasia. Compliance mismatch is a mismatch in mechanical properties that results when a relatively rigid stent is inserted within a more flexible vessel. Compliance mismatch is a particular problem at the ends of the stent where the radial flexibility of the vessel abruptly changes due to the rigidity of an expanded stent. One of the consequences of compliance mismatch in a vessel is local blood flow alteration. For example, the presence of the stent in the vessel produces complex flow patterns that include vortices, which may lead to platelet activation, and flow stagnation, which may be related to platelet adhesion through increased near-wall particle residence time. Accordingly, a substantial mismatch between the circumferential compliance of arterial grafts or stents and contiguous native vessels may be deleterious to vessel patency. Accordingly, it would be desirable to reduce the problems associated with compliance mismatch.